Calcineurin-induced energy wasting in a transgenic mouse model of heart failure.

Overexpression of calcineurin (CLN) in the mouse heart induces severe hypertrophy that progresses to heart failure, providing an opportunity to define the relationship between energetics and contractile performance in the severely failing mouse heart. Contractile performance was studied in isolated hearts at different pacing frequencies and during dobutamine challenge. Energetics were assessed by 31P-NMR spectroscopy as ATP and phosphocreatine concentrations ([ATP] and [PCr]) and free energy of ATP hydrolysis (|Delta G( approximately ATP)|).

Availability of 11-cis retinal and opsins without chromophore as revealed by small bleaches of rhodopsin in excised albino mouse eyes.

Small bleaches were used to study the rhodopsin regeneration process. At bleaches from 5.2% to 24.

Altered rhodopsin regeneration in diabetic mice caused by acid conditions within the rod photoreceptors.

Purpose: The experiments were designed to provide details on the characteristics of rhodopsin regeneration in the rod photoreceptors of diabetic mice and to evaluate their mechanistic basis.

Methods: A genetically-derived diabetic albino mouse was developed. An excised albino mouse eye preparation was used.

Decreased rhodopsin regeneration in diabetic mouse eyes.

Purpose: To evaluate the effect of diabetes on rhodopsin regeneration in the excised mouse eye.

Methods: A superfused excised mouse eye preparation that exhibits rhodopsin regeneration after moderate bleaches and that is responsive to the composition of the perfusate was used. Diabetes was induced in albino mice (BALB/c) with the diabetogenic agent streptozotocin.

Hypoxia inhibits rhodopsin regeneration in the excised mouse eye.

Purpose: The goal of this study was to evaluate the effect of oxygen deprivation on rhodopsin regeneration in the excised mouse eye.

Methods: A new preparation for studying rhodopsin regeneration with a superfused excised albino mouse eye was developed. The preparation exhibits multiple regenerations after moderate bleaches (15%-20%) and is sensitive to the composition of the perfusate, allowing reversible testing of conditions.

Extracellular glucose dependence of rhodopsin regeneration in the excised mouse eye.

To study the process of rhodopsin regeneration a superfused excised whole eye preparation of the albino mouse was developed. With this preparation, complete regeneration could be observed after each of the first two illuminations (bleaching 15-20%), and incomplete regeneration after a third illumination. Regeneration was minimal at extracellular glucose concentrations of 0 or 1 mM with improved regenerations at higher concentrations.

A stage in glycolysis controls the metabolic adjustments of vertebrate rod photoreceptors upon illumination.

The factors affecting the metabolic adjustments of toad rod photoreceptors were studied by monitoring the oxygen utilization of excised retinas and by measuring rod outer segment ATP and GTP concentrations. Respiratory adjustments upon illumination were observed when glucose or fructose was provided in the perfusate, but not when a glycolytic inhibitor was added to the perfusate containing glucose and pyruvate, or when a substrate beyond glycolysis or from a later stage of glycolysis was substituted for glucose. The amplitudes of the respiratory adjustments to illumination were dependent on the concentration of glucose in the perfusate.

Studies of the Drosophila norpA phototransduction mutant. II. Photoreceptor degeneration and rhodopsin maintenance.

The norpAH44 phototransduction mutant of Drosophila melanogaster, an allele that, on eclosion, does not exhibit a receptor potential was found, at later ages, to undergo light and temperature dependent degeneration of its photoreceptors as well as decreases in rhodopsin concentration. Pseudopupil measurements and light and electron microscopy were used to monitor the structure of the photoreceptors. When norpAH44 flies were maintained exclusively in the dark, no changes in structure or rhodopsin concentration were observed.

Studies of the Drosophila norpA phototransduction mutant. I. Electrophysiological changes and the offsetting effect of light.

The electrophysiological characteristics of norpAH52, a temperature sensitive phototransduction mutant of Drosophila melanogaster, were studied in vivo. Upon raising the environmental temperature to 33-37 degrees C, mutant flies exhibited time-dependent changes in photoresponses. Initial observations were losses in responsiveness at low light intensities and prolonged receptor potential waveforms.

Factors affecting the regeneration of rhodopsin in the isolated amphibian retina.

The capacity of isolated perfused frog and toad retinas to regenerate rhodopsin after a series of low level bleaches was investigated. For bleaches of less than 2% complete regeneration was observed after the first bleach with less or no regeneration after subsequent bleaches. Total regeneration from all bleaches was approximately 3%, an amount consistent with stores of 11-cis retinol in amphibian rod outer segments.

The effects of hepes, bicarbonate and calcium on the cGMP content of vertebrate rod photoreceptors and the isolated electrophysiological effects of cGMP and calcium.

To evaluate the role of cGMP in vertebrate rod photoreceptors, two extracellular effectors of cGMP were used (calcium and buffer), and both cGMP content and electrophysiological responses were measured. In the dark when the cGMP content was reduced by 80%, electrophysiological effects mimicking a weak background light were observed. Continuous illumination, sufficient to suppress all electrophysiological responses, had only minor effects on cGMP.

Pathways in the hydrolysis of vertebrate rhodopsin.

A direct method for measuring the amount of retinal 387 was used along with spectral techniques to measure each of the intermediates in the photolysis of rhodopsin and to unequivocally determine the pathways in solution extracts of bovine rhodopsin and excised toad and skate retinas. Metarhodopsin II 380 was the earliest intermediate which hydrolyzed to retinal 387 plus opsin. In excised toad retinas three approaches were used to show that Meta III 465 decayed directly to retinal 387 plus opsin.

Renewal of opsin in the photoreceptor cells of the mosquito.

Mosquito rhodopsin is a digitonin-soluble membrane protein of molecular weight 39,000 daltons, as determined by sodium dodecyl sulfate gel electrophoresis. The rhodopsin undergoes a spectral transition from R515-520 to M480 after orange illumination. The visual pigment apoprotein, opsin, is the major membrane protein in the eye.

Characteristics of Drosophila rhodopsin in wild-type and norpA vision transduction mutants.

The properties of the major visual pigment of Drosophila melanogaster were evaluated. The visual pigment was isolated from other protein components using acrylamide gel electrophoresis and spectral identification. Sodium dodecyl sulfate (SDS) acrylamide gels of the isolated visual pigment gave a single protein subunit with a mol wt of 37,000 daltons.

Ionizable groups and conductances of the rod photoreceptor membrane.

The ionizable groups and conductances of the rod plasma membrane were studied by measuring membrane potential and input impedance with micropipettes that were placed in the rod outer segments. Reduction of the pH from 8.0 to 6.

Electrical and adaptive properties of rod photoreceptors in Bufo marinus. I. Effects of altered extracellular Ca2+ levels.

The effects of altering extracellular Ca(2+) levels on the electrical and adaptive properties of toad rods have been examined. The retina was continually superfused in control (1.6 mM Ca(2+)) or test ringer's solutions, and rod electrical activity was recorded intracellularly.